Communication device, information processing method, and storage medium

ABSTRACT

A communication device includes: a plurality of wireless communication sections, each of which is configured to wirelessly receive a signal from another communication device; and a control section configured to detect a specific element in chronological information based on respective pulse signals received by the plurality of wireless communication sections, on the basis of respective pieces of chronological information including, as elements related to time, information that chronologically changes and that is obtained when the plurality of wireless communication sections receive the respective pulse signals transmitted from the other communication device, verify whether each of a plurality of the detected specific elements is based on the pulse signal coming through a shortest path, and estimate an angle from which the pulse signal has come while using axes extending from reference point, on the basis of the plurality of specific elements that are verified as elements based on the pulse signals.

CROSS REFERENCE TO RELATED APPLICATION(S)

This application is based upon and claims benefit of priority fromJapanese Patent Application No. JP2020-023213, filed on Feb. 14, 2020,the entire contents of which are incorporated herein by reference.

BACKGROUND

The present invention relates to a communication device, an informationprocessing method, and a storage medium.

In recent years, technologies that allow one device to estimate aposition of another device in accordance with a result oftransmitting/receiving a signal between the devices have been developed.As an example of the technologies of estimating a position, WO2015/176776 A1 discloses a technology that allows an UWB(ultra-wideband) receiver to estimate an angle of incidence of awireless signal from an UWB transmitter by performing wirelesscommunication using UWB.

However, the technology disclosed by WO 2015/176776 A1 has a problem ofreduction in accuracy of estimating the angle of incidence of thewireless signal in an environment where an obstacle is interposedbetween the transmitter and the receiver, or other environments.

Accordingly, the present invention is made in view of the aforementionedissues, and an object of the present invention is to provide a mechanismthat makes it possible to improve accuracy of estimating a position.

SUMMARY

To solve the above described problem, according to an aspect of thepresent invention, there is provided a communication device comprising:a plurality of wireless communication sections, each of which isconfigured to wirelessly receive a signal from another communicationdevice; and a control section configured to perform a first process ofdetecting a specific element that is a certain element in chronologicalinformation based on respective pulse signals received by the pluralityof wireless communication sections, on a basis of respective pieces ofchronological information including, as elements related to time,information that chronologically changes and that is obtained when theplurality of wireless communication sections receive the respectivepulse signals, which are signals including a pulse transmitted from theother communication device, perform a second process of verifyingwhether each of a plurality of the specific elements detected throughthe first process is based on the pulse signal coming through a shortestpath from the other communication device to each of the plurality ofwireless communication sections, and perform a third process ofestimating an angle from which the pulse signal has come while usingaxes extending from reference point, which is set to the plurality ofwireless communication sections, as reference axes, on a basis of theplurality of specific elements that are verified as elements based onthe pulse signals coming through the shortest path among the specificelements in the chronological information based on the respective pulsesignals received by the plurality of wireless communication sections.

To solve the above described problem, according to another aspect of thepresent invention, there is provided an information processing methodthat is performed by a communication device including a plurality ofwireless communication sections, each of which is configured towirelessly receive a signal from another communication device, theinformation processing method comprising: performing a first process ofdetecting a specific element that is a certain element in chronologicalinformation based on respective pulse signals received by the pluralityof wireless communication sections, on a basis of respective pieces ofchronological information including, as the elements related to time,information that chronologically changes and that is obtained when theplurality of wireless communication sections receive the respectivepulse signals, which are signals including a pulse transmitted from theother communication device; performing a second process of verifyingwhether each of a plurality of the specific elements detected throughthe first process is based on the pulse signal coming through a shortestpath from the other communication device to each of the plurality ofwireless communication sections; and performing a third process ofestimating an angle from which the pulse signal has come while usingaxes extending from reference point, which is set to the plurality ofwireless communication sections, as reference axes, on a basis of theplurality of specific elements that are verified as elements based onthe pulse signals coming through the shortest path among the specificelements in the chronological information based on the respective pulsesignals received by the plurality of wireless communication sections.

To solve the above described problem, according to another aspect of thepresent invention, there is provided a storage medium having a programstored therein, the program causing a computer for controlling acommunication device including a plurality of wireless communicationsections, each of which is configured to wirelessly receive a signalfrom another communication device, to function as a control sectionconfigured to perform a first process of detecting a specific elementthat is a certain element in chronological information based onrespective pulse signals received by the plurality of wirelesscommunication sections, on a basis of respective pieces of chronologicalinformation including, as the elements related to time, information thatchronologically changes and that is obtained when the plurality ofwireless communication sections receive the respective pulse signals,which are signals including a pulse transmitted from the othercommunication device, perform a second process of verifying whether eachof a plurality of the specific elements detected through the firstprocess is based on the pulse signal coming through a shortest path fromthe other communication device to each of the plurality of wirelesscommunication sections, and perform a third process of estimating anangle from which the pulse signal has come while using axes extendingfrom reference point, which is set to the plurality of wirelesscommunication sections, as reference axes, on a basis of the pluralityof specific elements that are verified as elements based on the pulsesignals coming through the shortest path among the specific elements inthe chronological information based on the respective pulse signalsreceived by the plurality of wireless communication sections.

As described above, according to the present invention, it is possibleto provide the mechanism that makes it possible to improve accuracy ofestimating a position.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an example of a configuration of asystem according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating an example of arrangement of aplurality of antennas installed in a vehicle according to theembodiment.

FIG. 3 is a diagram illustrating an example of a positional parameter ofa portable device according to the embodiment.

FIG. 4 is a diagram illustrating an example of a positional parameter ofthe portable device according to the embodiment.

FIG. 5 is a diagram illustrating an example of processing blocks forsignal processing in a communication unit according to the embodiment.

FIG. 6 is a graph illustrating an example of CIR according to theembodiment.

FIG. 7 is a sequence diagram illustrating an example of a flow of aranging process executed in the system according to the embodiment.

FIG. 8 is a sequence diagram illustrating an example of a flow of anangle estimation process executed in the system according to theembodiment.

FIG. 9 is a sequence diagram for describing an example of the positionestimation communication performed in the system according to thepresent embodiment.

FIG. 10 is a flowchart illustrating an example of a flow of a processexecuted by a communication unit 200 according to the embodiment.

DETAILED DESCRIPTION OF THE EMBODIMENT(S)

Hereinafter, referring to the appended drawings, preferred embodimentsof the present invention will be described in detail. It should be notedthat, in this specification and the appended drawings, structuralelements that have substantially the same function and structure aredenoted with the same reference numerals, and repeated explanationthereof is omitted.

Further, in the present specification and the drawings, differentalphabets are suffixed to a same reference numeral to distinguishelements which have substantially the same functional configuration. Forexample, a plurality of elements which have substantially the samefunctional configuration are distinguished such as wirelesscommunication sections 210A, 210B, and 210C, as necessary. However, whenthere is no need in particular to distinguish structural elements thathave substantially the same functional configuration, the same referencenumeral alone is attached. For example, in a case in which it is notnecessary to particularly distinguish the wireless communicationsections 210A, 210B, and 210C, the wireless communication sections 210A,210B, and 210C are simply referred to as the wireless communicationsections 210.

1. Configuration Example

FIG. 1 is a diagram illustrating an example of a configuration of asystem 1 according to an embodiment of the present invention. Asillustrated in FIG. 1, the system 1 according to the present embodimentincludes a portable device 100 and a communication unit 200. Thecommunication unit 200 according to the present embodiment is installedin a vehicle 202. The vehicle 202 is an example of a usage target of theuser.

A communication device of an authenticatee and a communication device ofan authenticator are involved in the present embodiment. In the exampleillustrated in FIG. 1, the portable device 100 is an example of thecommunication device of the authenticatee, and the communication unit200 is an example of the communication device of the authenticator.

When a user (for example, a driver of the vehicle 202) carrying theportable device 100 approaches the vehicle 202, the system 1 performswireless communication for authentication between the portable device100 and the communication unit 200 installed in the vehicle 202. Next,when the authentication succeeds, the vehicle 202 becomes available forthe user by unlocking a door lock of the vehicle 202 or starting anengine of the vehicle 202. The system 1 is also referred to as a smartentry system. Next, respective structural elements will be describedsequentially.

(1) Portable Device 100

The portable device 100 is configured as any device to be carried by theuser. Examples of the any device include an electronic key, asmartphone, a wearable terminal, and the like. As illustrated in FIG. 1,the portable device 100 includes a wireless communication section 110, astorage section 120, and a control section 130.

The wireless communication section 110 has a function of performingwireless communication with the communication unit 200 installed in thevehicle 202. The wireless communication section 110 wirelessly receivesa signal from the communication unit 200 installed in the vehicle 202.In addition, the wireless communication section 110 wirelessly transmitsa signal to the communication unit 200.

Wireless communication is performed between the wireless communicationsection 110 and the communication unit 200 by using an ultra-wideband(UWB) signal, for example. In the wireless communication of the UWBsignal, it is possible for impulse UWB to measure propagation delay timeof a radio wave with high accuracy by using the radio wave ofultra-short pulse width of a nanosecond or less, and it is possible toperform ranging with high accuracy on the basis of the propagation delaytime. Note that, the propagation delay time is time from transmission toreception of the radio wave. The wireless communication section 110 isconfigured as a communication interface that makes it possible toperform communication by using the UWB signals, for example.

Note that, the UWB signal may be transmitted/received as a rangingsignal, an angle estimation signal, and a data signal, for example. Theranging signal is a signal transmitted and received in the rangingprocess (to be described later). The ranging signal may be configured ina frame format that does not include a payload part for storing data orin a frame format that includes the payload part. The angle estimationsignal is a signal transmitted and received in an angle estimationprocess (to be described later). The angle estimation signal may beconfigured in a way similar to the ranging signal. The data signal ispreferably configured in the frame format that includes the payload partfor storing the data.

Here, the wireless communication section 110 includes at least oneantenna 111. In addition, the wireless communication section 110transmits/receives a wireless signal via the at least one antenna 111.

The storage section 120 has a function of storing various kinds ofinformation for operating the portable device 100. For example, thestorage section 120 stores a program for operating the portable device100, and an identifier (ID), password, and authentication algorithm forauthentication, or the like. For example, the storage section 120includes a storage medium such as flash memory and a processing devicethat performs recording/playback on/of the storage medium.

The control section 130 has a function of executing processes in theportable device 100. For example, the control section 130 controls thewireless communication section 110 to perform communication with thecommunication unit 200 of the vehicle 202. The control section 130 readsinformation from the storage section 120 and writes information into thestorage section 120. The control section 130 also functions as anauthentication control section that controls an authentication processbetween the portable device 100 and the communication unit 200 of thevehicle 202. For example, the control section 130 may include a centralprocessing unit (CPU) and an electronic circuit such as amicroprocessor.

(2) Communication Unit 200

The communication unit 200 is prepared in association with the vehicle202. Here, it is assumed that the communication unit 200 is installed inthe vehicle 202 in such a manner that communication section 200 isinstalled in a vehicle interior of the vehicle 202, the communicationsection 200 is built in the vehicle 202 as a communication module, or inother manners. Alternatively, the communication unit 200 may be preparedas a separate object from the vehicle 202 in such a manner that thecommunication unit 200 is installed in a parking space for the vehicle202 or in other manners. In this case, the communication unit 200 maywirelessly transmit a control signal to the vehicle 202 on the basis ofa result of communication with the portable device 100 and may remotelycontrol the vehicle 202. As illustrated in FIG. 1, the communicationunit 200 includes a plurality of wireless communication sections 210(210A to 210D), a storage section 220, and a control section 230.

The wireless communication section 210 has a function of performingwireless communication with the wireless communication section 110 ofthe portable device 100. The wireless communication section 210wirelessly receives a signal from the portable device 100. In addition,the wireless communication section 210 wirelessly transmits a signal tothe portable device 100. The wireless communication section 210 isconfigured as a communication interface that makes it possible toperform communication by using the UWB signals, for example.

Here, each of the wireless communication sections 210 includes anantenna 211. In addition, each of the wireless communication sections210 transmits/receives a wireless signal via the antenna 211.

The storage section 220 has a function of storing various kinds ofinformation for operating the communication unit 200. For example, thestorage section 220 stores a program for operating the communicationunit 200, an authentication algorithm, and the like. For example, thestorage section 220 includes a storage medium such as flash memory and aprocessing device that performs recording/playback on/of the storagemedium.

The control section 230 has a function of controlling overall operationperformed by the communication unit 200 and in-vehicle equipmentinstalled in the vehicle 202. For example, the control section 230controls the wireless communication sections 210 to performcommunication with the portable device 100. The control section 230reads information from the storage section 220 and writes informationinto the storage section 220. The control section 230 also functions asan authentication control section that controls the authenticationprocess between the portable device 100 and the communication unit 200.In addition, the control section 230 also functions as a door lockcontrol section that controls the door key of the vehicle 202, and locksand unlocks doors with the door key. The control section 230 alsofunctions as an engine control section that controls the engine of thevehicle 202, and starts/stops the engine. Note that, a motor or the likemay be installed as a power source in the vehicle 202 in addition to theengine. For example, the control section 230 is configured as anelectronic circuit such as an electronic control unit (ECU).

2. Estimation of Positional Parameter

<2.1. Positional Parameter>

The communication unit 200 (specifically, control section 230) accordingto the present embodiment performs a positional parameter estimationprocess of estimating a positional parameter that represents a positionof the portable device 100. Hereinafter, with reference to FIG. 2 toFIG. 4, various definitions related to the positional parameter will bedescribed.

FIG. 2 is a diagram illustrating an example of arrangement of theplurality of antennas 211 (wireless communication sections 210)installed in the vehicle 202 according to the present embodiment. Asillustrated in FIG. 2, the four antennas 211 (211A to 211D) areinstalled on a ceiling of the vehicle 202. The arrangement positions ofthe antennas 211 are arrangement positions of the wireless communicationsections 210. The antenna 211A is installed on a front right side of thevehicle 202. The antenna 211B is installed on a front left side of thevehicle 202. The antenna 211C is installed on a rear right side of thevehicle 202. The antenna 211D is installed on a rear left side of thevehicle 202. Note that, a distance between adjacent antennas 211 are setto half or less of wavelength X of a carrier wave of an angle estimationsignal (to be described later). A local coordinate system of thecommunication unit 200 is set as a coordinate system based on thecommunication unit 200. An example of the local coordinate system of thecommunication unit 200 has its origin at the center of the four antennas211. This local coordinate system has its X axis along a front-reardirection of the vehicle 202, its Y axis along a left-right direction ofthe vehicle 202, and its Z axis along an up-down direction of thevehicle 202. Note that, the X axis is parallel to a line connecting apair of the antennas in the front-rear direction (such as a pair of theantenna 211A and the antenna 211C, and a pair of the antenna 211B andthe antenna 211D). In addition, the Y axis is parallel to a lineconnecting a pair of the antennas in the left-right direction (such as apair of the antenna 211A and the antenna 211B, and a pair of the antenna211C and the antenna 211D).

Note that, the arrangement of the four antennas is not limited to thesquare shape. The arrangement of the four antennas may be aparallelogram shape, a trapezoid shape, a rectangular shape, or anyother shapes. Of course, the number of antennas 211 is not limited tofour.

FIG. 3 is a diagram illustrating an example of positional parameters ofthe portable device 100 according to the present embodiment. Thepositional parameters may include a distance R between the portabledevice 100 and the communication unit 200. The distance R illustrated inFIG. 3 is a distance from the origin of the local coordinate system ofthe communication unit 200 to the portable device 100. The distance R isestimated on the basis of a result of transmission/reception of aranging signal (to be described later) between the portable device 100and one of the plurality of wireless communication sections 210. Thedistance R may be a distance between the portable device 100 and thesingle wireless communication section 210 that transmits/receives theranging signal (to be described later).

In addition, as illustrated in FIG. 3, the positional parameters mayinclude an angle of the portable device 100 based on the communicationunit 200, the angle including an angle α between the X axis and theportable device 100 and an angle β between the Y axis and the portabledevice 100. The angles α and β are angles between the coordinate axes ofa first predetermined coordinate system and a straight line connectingthe portable device 100 with the origin on the first predeterminedcoordinate system. For example, the first predetermined coordinatesystem is the local coordinate system of the communication unit 200. Theangle α is an angle between the X axis and the straight line connectingthe portable device 100 with the origin. The angle β is an angle betweenthe Y axis and the straight line connecting the portable device 100 withthe origin.

FIG. 4 is a diagram illustrating an example of positional parameters ofthe portable device 100 according to the present embodiment. Thepositional parameters may include coordinates of the portable device 100in a second predetermined coordinate system. In FIG. 4, a coordinate xon the X axis, a coordinate y on the Y axis, and a coordinate z on the Zaxis of the portable device 100 are an example of such coordinates. Inother words, the second predetermined coordinate system may be the localcoordinate system of the communication unit 200. Alternatively, thesecond predetermined coordinate system may be a global coordinatesystem.

<2.2. CIR>

(1) CIR Calculation Process

In the positional parameter estimation process, the portable device 100and the communication unit 200 communicate with each other to estimatethe positional parameters. At this time, the portable device 100 and thecommunication unit 200 calculates channel impulse responses (CIRs).

The CIR is a response obtained when an impulse is input to the system.In the case where a wireless communication section of one of theportable device 100 and the communication unit 200 (hereinafter, alsoreferred to as a transmitter) transmits a signal including a pulse, theCIR according to the present embodiment is calculated on the basis ofthe signal received by a wireless communication section of the other(hereinafter, also referred to as a receiver). The pulse is a signalincluding variation in amplitude. Hereinafter, a signal transmitted fromthe transmitter is referred to as a transmission signal. In addition, asignal received by the receiver is referred to as a reception signal.

Here, sometimes the reception signal is different from the transmissionsignal due to influence of the obstacle or the like interposed betweenthe transmitter and the receiver. The CIR is calculated on the basis ofthe transmission signal and the reception signal. In other words, theCIR is calculated on the basis of the reception signal that is a signalthat corresponds to the transmission signal and that is received by thewireless communication section of the receiver in the case where thewireless communication section of the transmitter transmits thetransmission signal. Note that, the transmission signal is known to thereceiver. It can be said that the CIR indicates characteristics of awireless communication path between the portable device 100 and thecommunication unit 200.

For example, the CIR may be a correlation computation result that is aresult obtained by correlating the transmission signal with thereception signal at each delay time that is time elapse after thetransmitter transmits the transmission signal. Here, the correlation maybe sliding correlation that is a process of correlating the transmissionsignal with the reception signal by shifting relative positions of thesignals in time directions. The correlation computation result includesa correlation value indicating a degree of the correlation between thetransmission signal and the reception signal as an element obtained ateach delay time. Each of a plurality of the elements included in thecorrelation computation result is information including a combination ofthe delay time and the correlation value. The correlation may becalculated at each delay time between designated intervals. In otherwords, the CIR may be a result of correlating the transmission signalwith the reception signal at the designated intervals after thetransmitter transmits the transmission signal. Here, the designatedinterval is an interval between timings at which the receiver samplesthe reception signal, for example. Therefore, an element included in theCIR is also referred to as a sampling point. The correlation valueincludes at least any of an amplitude component and a phase component.The amplitude component is amplitude or electric power obtained bysquaring the amplitude. The phase component is an angle between IQcomponents of a CIR and an I axis on an IQ plane. The phase componentmay be simply referred to as a phase. The correlation value may be acomplex number including the IQ components.

A value obtained at each delay time of the CIR is also referred to as aCIR value. In other words, the CIR is chronological variation in the CIRvalue. In the case where the CIR is the correlation computation result,the CIR value is a correlation value obtained at each delay time.

In the case where the CIR is the correlation computation result, thereceiver calculates the CIR by correlating the transmission signal withthe reception signal through the sliding correlation. For example, thereceiver calculates a value obtained by correlating the reception signalwith the transmission signal delayed by a certain delay time, ascharacteristics (that is, a CIR value) at the delay time. Next, thereceiver calculates the CIR value at each delay time to calculate theCIR. Hereinafter, it is assumed that the CIR is the correlationcomputation result.

Note that, the CIR is also referred to as delay profile in a rangingtechnology using the UWB. In particular, the CIR using electric power asthe CIR value is referred to as power delay profile.

Hereinafter, with reference to FIG. 5 to FIG. 6, a CIR calculationprocess performed in the case where the portable device 100 serves asthe transmitter and the communication unit 200 serves as the receiverwill be described in detail.

FIG. 5 is a diagram illustrating an example of processing blocks forsignal processing in the communication unit 200 according to the presentembodiment. As illustrated in FIG. 5, the communication unit 200includes an oscillator 212, a multiplier 213, a 90-degree phase shifter214, a multiplier 215, a low pass filter (LPF) 216, a LPF 217, acorrelator 218, and an integrator 219.

The oscillator 212 generates a signal of same frequency as frequency ofa carrier wave that carries a transmission signal, and outputs thegenerated signal to the multiplier 213 and the 90-degree phase shifter214.

The multiplier 213 multiplies a reception signal received by the antenna211 and the signal output from the oscillator 212, and outputs a resultof the multiplication to the LPF 216. Among input signals, the LPF 216outputs a signal of lower frequency than the frequency of the carrierwave that carries the transmission signal, to the correlator 218. Thesignal input to the correlator 218 is an I component (that is, a realpart) among components corresponding to an envelope of the receptionsignal.

The 90-degree phase shifter 214 delays the phase of the input signal by90 degrees, and outputs the delated signal to the multiplier 215. Themultiplier 215 multiplies the reception signal received by the antenna211 and the signal output from the 90-degree phase shifter 214, andoutputs a result of the multiplication to the LPF 217. Among inputsignals, the LPF 217 outputs a signal of lower frequency than thefrequency of the carrier wave that carries the transmission signal, tothe correlator 218. The signal input to the correlator 218 is a Qcomponent (that is, an imaginary part) among the componentscorresponding to the envelope of the reception signal.

The correlator 218 calculates the CIR by correlating a reference signalwith the reception signals including the I component and the Q componentoutput from the LPF 216 and the LPF 217 through the sliding correlation.Note that, the reference signal described herein is the same signal asthe transmission signal before multiplying the carrier wave.

The integrator 219 integrates the CIRs output from the correlator 218,and outputs the integrated CIRs.

Here, the transmitter may transmit a signal including a preamble as thetransmission signal. The preamble is a sequence known to the transmitterand the receiver. Typically, the preamble is arranged at a head of thetransmission signal. The preamble includes one or more preamble symbols.The preamble symbol is a pulse sequence including one or more pulses.The pulse sequence is a set of the plurality of pulses that are separatefrom each other in the time direction.

The preamble symbol is a target of integration performed by theintegrator 219. Therefore, the correlator 218 calculates the CIR foreach of the one or more preamble symbols by correlating a portioncorresponding to a preamble symbol included in the reception signal witha preamble symbol included in the transmission signal with regard toeach of portions corresponding to the one or more preamble symbolsincluded in the reception signal, at the designated intervals after theportable device 100 transmits the preamble symbol. Next, the integrator219 obtains integrated CIRs by integrating the CIRs of the respectivepreamble symbols with regard to the one or more preamble symbolsincluded in the preamble. Next, the integrator 219 outputs theintegrated CIRs. Hereinafter, the CIR means the integrated CIRs unlessotherwise noted.

The CIR of each preamble symbol is an example of the first correlationcomputation result. The integrated CIRs are an example of the secondcorrelation computation result. As described above, the CIR includes acorrelation value indicating a degree of the correlation between thetransmission signal and the reception signal as an element obtained ateach delay time, which is time elapsed after the transmitter transmitsthe transmission signal. From a viewpoint of the preamble symbol, theCIR includes the correlation value indicating a degree of thecorrelation between the transmission signal and the reception signal asan element obtained at each delay time, which is time elapsed after thetransmitter transmits each preamble symbol.

Here, the portable device 100 and the communication unit 200 acquiretime by using a time counter. The time counter is a counter foracquiring time. The counter is a counting function. A value of the timecounter (hereinafter, referred to as a counter value) is incrementedeach time unit time elapses. The unit time is prescribed period of time.This allows the portable device 100 and the communication unit 200 toacquire time on the basis of the counter value and the unit time. Notethat, here, the time is relative time based on criterial time. Forexample, the criterial time is time acquired when the counter value iszero. In addition, for example, the unit time is the designatedinterval.

A time counter of the portable device 100 may be synchronous with a timecounter of the communication unit 200. The case where the time countersare synchronous with each other means that they have identical unit timeand criterial time. The time counter of the portable device 100 may benon-synchronous with the time counter of the communication unit 200. Thecase where the time counters are no-synchronous with each other meansdisagreement between the portable device 100 and the communication unit200 over at least any of the unit time or the criterial time.

The time counters of the plurality of wireless communication sections210 may be synchronous with each other. In the case where the timecounters are not synchronous with each other, time axes of a pluralityof CIRs calculated with regard to the plurality of wirelesscommunication sections 210 are also non-synchronous with each other(that is, the time axes are not identical). The time counters of theplurality of wireless communication sections 210 may be non-synchronouswith each other. In the case where the time counters are synchronouswith each other, the time axes of the plurality of CIRs calculated withregard to the plurality of wireless communication sections 210 are alsosynchronous with each other (that is, the time axes are identical).

Time acquired using the time counters corresponds to the above-describeddelay time. This is because the delay time is time obtained bysubtracting time when the transmitter transmits the transmission signalfrom time acquired from the time counters. Therefore, the CIR may betreated as chronological variation in the CIR values obtained atrespective points of time acquired from the time counters. In this case,a time axis of CIR of respective preamble symbols of a preamble symbolthat is initially received is used as a time axis of the integratedCIRs.

(2) Example of CIR

FIG. 6 illustrates an example of the CIR output from the integrator 219.FIG. 6 is a graph illustrating the example of CIR according to thepresent embodiment. The graph includes a horizontal axis representingdelay time. The graph includes a vertical axis representing absolutevalues of CIR values (such as amplitude or electric power). Note that,the shape of CIR, more specifically, the shape of chronological changein the CIR value may also be referred to as a CIR waveform. Typically, aset of elements obtained between a zero-crossing and anotherzero-crossing corresponds to a single pulse with regard to the CIR. Thezero-crossing is an element whose value is zero. However, the same doesnot apply to an environment with noise. For example, a set of elementsobtained between intersections of a standard with chronologicalvariation in the CIR value may be treated as corresponding to the singlepulse. The CIR illustrated in FIG. 6 include a set 21 of elementscorresponding to a certain pulse, and a set 22 of elements correspondingto another pulse.

Here, sometimes multipath may be caused. The multipath is a situationwhere a receiver receives a plurality of radio waves transmitted from asingle transmitter. The multipath is caused in the case where there area plurality of paths between the transmitter and the receiver. In thecase where the multipath is caused, sometimes signals that have passedthrough different paths arrive at the receiver at different timing, orthe signal may arrive at overlapping timings and may be received in astate where the signals interfere with each other.

For example, the set 21 corresponds to a signal (such as pulse) thatreaches the receiver through a first path. The first path is a shortestpath between the transmitter and the receiver. In an environment thatincludes no obstacle, the first path is a straight path between thetransmitter and the receiver. For example, the set 22 corresponds to asignal (such as pulse) that reaches the receiver through a path otherthan the first path. As described above, the signals that have passedthrough different paths are also referred to as multipath waves.

(3) Detection of First Incoming Wave

Among wireless signals received from the transmitter, the receiverdetects a signal that meets a predetermined detection standard as asignal that reaches the receiver through the first path. Next, thereceiver estimates the positional parameters on the basis of thedetected signal.

Hereinafter, the signal detected as the signal that reaches the receiverthrough the first path is also referred to as the first incoming wave.The first incoming wave may be any of a direct wave, a delayed wave, ora combined wave. The direct wave is a signal that passes through ashortest path between the transmitter and the receiver, and is receivedby the receiver. In other words, the direct wave is a signal thatreaches the receiver through the first path. The delayed wave is asignal that passes through a path different from the shortest pathbetween the transmitter and the receiver, that is, through a path otherthan the first path. The delayed wave is received by the receiver aftergetting delayed in comparison with the direct wave. The combined wave isa signal received by the receiver in a state of combining a plurality ofsignals that have passed through a plurality of different paths.

The receiver detects a signal that meets a predetermined detectionstandard as the first incoming wave, among the received wirelesssignals. For example, the predetermined detection standard is acondition that the CIR value (such as amplitude or electric power)exceeds a predetermined threshold for the first time. In other words,the receiver may detect a pulse corresponding to a portion of the CIRobtained when the CIR value exceeds the predetermined threshold for thefirst time, as the first incoming wave.

Here, it should be noted that the signal detected as the first incomingwave is not necessarily the direct wave. For example, if the direct waveis received in a state where the direct wave and the delayed waveannihilate each other, sometimes the CIR value falls below thepredetermined threshold and the direct wave is not detected as the firstincoming wave. In this case, the combined wave or the delayed wavecoming while being delayed behind the direct wave is detected as thefirst incoming wave.

Hereinafter, the predetermined threshold used for detecting the firstincoming wave is also referred to as a first path threshold.

Reception Time of First Incoming Wave

The receiver may treat the time of meeting the predetermined detectionstandard as the time of receiving the first incoming wave. For example,the reception time of the first incoming wave is time corresponding todelayed time of an element whose CIR value exceeds the first paththreshold for the first time.

Alternatively, the receiver may treat time of obtaining a peak of thedetected first incoming wave as the reception time of the first incomingwave. In this case, for example, the reception time of the firstincoming wave is time corresponding to delayed time of an element havinghighest amplitude or electric power as the CIR value, among the set ofelements corresponding to the first incoming wave with regard to theCIR.

Here, the wireless communication section 210 receives a plurality ofpulses that are transmitted as the transmission signals from theportable device 100 through a plurality of paths, as the receptionsignals. The reception time of the first incoming wave is pulsereception time that is time when the wireless communication section 210receives a pulse included in the reception signal. In particular, it canbe said that the reception time of the first incoming wave is pulsereception time of a pulse detected for the first time, among theplurality of pulses coming through the plurality of paths.

Hereinafter, it is assumed that the reception time of the first incomingwave is time corresponding to delayed time of an element whose CIR valueexceeds the first path threshold for the first time.

Phase of First Incoming Wave

The receiver may treat a phase obtained at time of meeting thepredetermined detection standard as a phase the first incoming wave. Forexample, the phase of the first incoming wave is a phase serving as aCIR value of an element whose CIR value exceeds the first path thresholdfor the first time.

Alternatively, the receiver may treat a phase of the peak of thedetected first incoming wave as the phase of the first incoming wave. Inthis case, for example, the phase of the first incoming wave is thephase serving as a CIR value of an element having highest amplitude orelectric power as the CIR value, among the set of elements correspondingto the first incoming wave with regard to the CIR.

Hereinafter, it is assumed that the phase of the first incoming wave isa phase serving as a CIR value of an element whose CIR value exceeds thefirst path threshold for the first time.

Width of First Incoming Wave

The width of the set of elements corresponding to the first incomingwave in the time direction is also referred to as the width of the firstincoming wave. For example, the width of the first incoming wave is thewidth between a zero-crossing and another zero-crossing of the CIR inthe time direction. For another example, the width of the first incomingwave is width between intersections of a standard with chronologicalvariation in the CIR value in the time direction.

The width of a pulse included in the transmission signal in the timedirection is also referred to as the width of the pulse. For example,the width of the pulse is the width between a zero-crossing and anotherzero-crossing of chronological variation in the CIR value in the timedirection. For another example, the width of the pulse is width betweenintersections of a standard with chronological variation in the CIRvalue in the time direction.

In the case where only the direct wave is detected as the first incomingwave, the first incoming wave of the CIR has an ideal width. The idealwidth obtained when only the direct wave is detected as the firstincoming wave can be calculated through theoretical calculation usingwaveform of the transmission signal, a reception signal processingmethod, and the like. On the other hand, in the case where a combinedwave is received as the first incoming wave, the width of the firstincoming wave of the CIR may be different from the ideal width. Forexample, in the case where a combined wave in which a delayed wavehaving a same phase as the direct wave and the direct wave are combinedis detected as the first incoming wave, a portion corresponding to thedirect wave and a portion corresponding to the delayed wave are added ina state where they are shifted in the time direction. Therefore, theportions reinforce each other, and the first incoming wave in the CIRhas a wider width. On the other hand, in the case where a combined wavein which a delayed wave having an opposite phase from the direct waveand the direct wave are combined is detected as the first incoming wave,the direct wave and the delayed wave annihilate each other. Therefore,the first incoming wave in the CIR has a narrower width.

<2.3. Estimation of Positional Parameter>

(1) Ranging

The communication unit 200 performs the ranging process. The rangingprocess is a process of estimating a distance between the communicationunit 200 and the portable device 100. For example, the distance betweenthe communication unit 200 and the portable device 100 is the distance Rillustrated in FIG. 3. The ranging process includestransmission/reception of a ranging signal and calculation of thedistance R based on propagation delay time of the ranging signal. Theranging signal is a signal used for ranging among signalstransmitted/received between the portable device 100 and thecommunication unit 200. The propagation delay time is time fromtransmission to reception of the signal.

Here, the ranging signal is transmitted/received by one of the pluralityof wireless communication sections 210 of the communication unit 200.Hereinafter, the wireless communication section 210 thattransmits/receives the ranging signal is also referred to as a master.The distance R is a distance between the wireless communication section210 serving as the master (more precisely, the antenna 211) and theportable device 100 (more precisely, the antenna 111). In addition, thewireless communication sections 210 other than the wirelesscommunication section 210 that transmits/receives the ranging signal arereferred to as slaves.

In the ranging process, a plurality of the ranging signals may betransmitted and received between communication unit 200 and the portabledevice 100. Among the plurality of ranging signals, a ranging signaltransmitted from one device to the other device is also referred to as afirst ranging signal. Next, a ranging signal transmitted as a responseto the first ranging signal from the device that has received the firstranging signal to the device that has transmitted the first rangingsignal is also referred to as a second ranging signal. In addition, aranging signal transmitted as a response to the second ranging signalfrom the device that has received the second ranging signal to thedevice that has transmitted the second ranging signal is also referredto as a third ranging signal.

Next, with reference to FIG. 7, an example of a flow of the rangingprocess will be described.

FIG. 7 is a sequence diagram illustrating the example of the flow of theranging process executed in the system 1 according to the presentembodiment. The portable device 100 and the communication unit 200 areinvolved in this sequence. It is assumed that the wireless communicationsection 210A functions as the master in this sequence.

As illustrated in FIG. 7, the portable device 100 first transmits thefirst ranging signal (Step S102). When the wireless communicationsection 210A receives the first ranging signal, the control section 230calculates a CIR of the first ranging signal. Next, the control section230 detects a first incoming wave of the first ranging signal of thewireless communication section 210A on the basis of the calculated CIR(Step S104).

Next, the wireless communication section 210A transmits the secondranging signal in response to the first ranging signal (Step S106). Whenthe second ranging signal is received, the portable device 100calculates a CIR of the second ranging signal. Next, the portable device100 detects a first incoming wave of the second ranging signal on thebasis of the calculated CIR (Step S108).

Next, the portable device 100 transmits the third ranging signal inresponse to the second ranging signal (Step S110). When the wirelesscommunication section 210A receives the third ranging signal, thecontrol section 230 calculates a CIR of the third ranging signal. Next,the control section 230 detects a first incoming wave of the thirdranging signal of the wireless communication section 210A on the basisof the calculated CIR (Step S112).

The portable device 100 measures time T₁ from transmission time of thefirst ranging signal to reception time of the second ranging signal, andtime T₂ from reception time of the second ranging signal to transmissiontime of the third ranging signal. Here, the reception time of the secondranging signal is reception time of the first incoming wave of thesecond ranging signal detected in Step S108. Next, the portable device100 transmits a signal including information indicating the time T₁ andthe time T₂ (Step S114). For example, such a signal is received by thewireless communication section 210A.

The control section 230 measures a time T₃ from reception time of thefirst ranging signal to transmission time of the second ranging signal,and time T₄ from transmission time of the second ranging signal toreception time of the third ranging signal. Here, the reception time ofthe first ranging signal is reception time of the first incoming wave ofthe first ranging signal detected in Step S104. In a similar way, thereception time of the third ranging signal is reception time of thefirst incoming wave of the third ranging signal detected in Step S112.

Next, the control section 230 estimates the distance R on the basis ofthe time periods T₁, T₂, T₃, and T₄ (Step S116). For example, thecontrol section 230 estimates propagation delay time τ_(m) by using anequation listed below.

$\begin{matrix}{\tau_{m} = \frac{{T_{1} \times T_{4}} - {T_{2} \times T_{3}}}{T_{1} + T_{2} + T_{3} + T_{4}}} & (1)\end{matrix}$

Next, the control section 230 estimates the distance R by multiplyingthe estimated propagation delay time τ_(m) by speed of the signal.

Cause of Reduction in Accuracy of Estimation

The reception times of the ranging signals serving as start or end ofthe time periods T₁, T₂, T₃, and T₄ are reception times of the firstincoming waves of the ranging signals. As described above, the signaldetected as the first incoming wave is not necessarily the direct wave.

In the case where the combined wave or the delayed wave coming whilebeing delayed behind the direct wave is detected as the first incomingwave, reception time of the first incoming wave varies in comparisonwith the case where the direct wave is detected as the first incomingwave. In this case, the propagation delay time τ_(m) is changed from atrue value (propagation delay time τ_(m) obtained in the case where thedirect wave is detected as the first incoming wave). In addition, thischange deteriorates accuracy of estimating the distance R (hereinafter,also referred to as ranging accuracy).

Specifically, in the case where the direct wave is not detected as thefirst incoming wave, the combined wave or the delayed wave coming whilebeing delayed behind the direct wave is detected as the first incomingwave. Therefore, the reception time of the first incoming wave isdelayed. As a result, the propagation delay time τ_(m) obtained in thecase where the direct wave is not detected as the first incoming wave islonger than the propagation delay time τ_(m) obtained in the case wherethe direct wave is detected as the first incoming wave. Next, becausethe propagation delay time τ_(m) is longer than the true value, thedistance R is estimated as a distance longer than the true value.

(2) Angle Estimation

The communication unit 200 performs the angle estimation process. Theangle estimation process is a process of estimating the angles α and βillustrated in FIG. 3. The angle estimation process includes receptionof an angle estimation signal and calculation of the angles α and β onthe basis of a result of reception of the angle estimation signal. Theangle estimation signal is a signal used for estimating an angle amongsignals transmitted/received between the portable device 100 and thecommunication unit 200. Next, with reference to FIG. 8, an example of aflow of the angle estimation process will be described.

FIG. 8 is a sequence diagram illustrating the example of the flow of theangle estimation process executed in the system 1 according to thepresent embodiment. The portable device 100 and the communication unit200 are involved in this sequence.

As illustrated in FIG. 8, the portable device 100 first transmits theangle estimation signal (Step S202). Next, when the wirelesscommunication sections 210A to 210D receive respective angle estimationsignals, the control section 230 calculates CIRs of the respective angleestimation signals received by the wireless communication sections 210Ato 210D. Next, the control section 230 detects first incoming waves ofthe respective angle estimation signals on the basis of the calculatedCIRs with regard to the wireless communication sections 210A to 210D(Step S204A to Step S204D). Next, the control section 230 detectsrespective phases of the detected first incoming waves with regard tothe wireless communication sections 210A to 210D (Step S206A to StepS206D). Next, the control section 230 estimates the angles α and β onthe basis of the respective phases of the detected first incoming waveswith regard to the wireless communication sections 210A to 210D (StepS208).

Next, details of a process in Step S208 will be described. PA representsthe phase of the first incoming wave detected with regard to thewireless communication section 210A. PB represents the phase of thefirst incoming wave detected with regard to the wireless communicationsection 210B. Pc represents the phase of the first incoming wavedetected with regard to the wireless communication section 210C. P_(D)represents the phase of the first incoming wave detected with regard tothe wireless communication section 210D. The wireless communicationsections 210A and 210C are a pair of two wireless communication sections210 disposed in the X axis direction. The wireless communicationsections 210B and 210D are a pair of two wireless communication sections210 disposed in the X axis direction. Each pair forms an antenna arrayin the X axis direction. The antenna array is a combination of aplurality of antennas. On the other hand, the wireless communicationsections 210A and 210B are a pair of two wireless communication sections210 disposed in the Y axis direction. The wireless communicationsections 210C and 210D are a pair of two wireless communication sections210 disposed in the Y axis direction. Each pair forms an antenna arrayin the Y axis direction. In this case, antenna array phase differencesPd_(AC) and Pd_(BD) in the X axis direction and antenna array phasedifferences Pd_(BA) and Pd_(DC) in the Y axis direction are expressed inrespective equations listed below. The antenna array phase difference isa difference between phases of the first incoming waves with regard totwo antennas 211 (that is, wireless communication sections 210) includedin the antenna array.

Pd _(AC)=(P _(A) −P _(C))

Pd _(BD)=(P _(B) −P _(D))

Pd _(DC)=(P _(D) −P _(C))

Pd _(BA)=(P _(B) −P _(A))  (2)

The angles α and β are calculated by using the following equation. Here,X represents wavelength of a carrier wave of the angle estimationsignal, and d represents a distance between the antennas 211.

α or β=arccos(λ·Pd/(2·π·d))  (3)

Therefore, respective equations listed below represent angles calculatedon the basis of the respective antenna array phase differences.

α_(AC)=arccos(λ·Pd _(AC)/(2·π·d))

α_(BD)=arccos(λ·Pd _(BD)/(2·π·d))

β_(DC)=arccos(λ·Pd _(DC)/(2·π·d))

β_(BA)=arccos(λ·Pd _(BA)/(2·π·d))  (4)

The control section 230 calculates the angles α and β on the basis ofthe calculated angles α_(AC), α_(BD), β_(DC), and β_(BA). For example,as expressed in the following equations, the control section 230calculates the angles α and β by averaging the angles calculated withregard to the two respective arrays in the X axis direction and the Yaxis direction.

α=(α_(AC)+α_(BD))/2

β=(β_(DC)+β_(BA))/2  (5)

Cause of Reduction in Accuracy of Estimation

As described above, the angles α and β are calculated on the basis ofthe phases of the first incoming waves. As described above, the signaldetected as the first incoming wave is not necessarily the direct wave.

In other words, sometimes the delayed wave or the combined wave may bedetected as the first incoming wave. Typically, phases of the delayedwave and the combined wave are different from the phase of the directwave. This difference deteriorates accuracy of angle estimation.

Supplement

Note that, the angle estimation signal may be transmitted/receivedduring the angle estimation process, or at any other timings. Forexample, the angle estimation signal may be transmitted/received duringthe ranging process. Specifically, the third ranging signal illustratedin FIG. 7 may be the same as the angle estimation signal illustrated inFIG. 8. In this case, it is possible for the communication unit 200 tocalculate the distance R, the angle α, and the angle β by receiving asingle wireless signal that serves as both the angle estimation signaland the third ranging signal.

In the above description, the receiver estimates the angle α byaveraging the angles α_(AC) and asp that are estimated on the basis ofthe difference between phases of the two antenna arrays in the Xdirection. The receiver may adopt any one of the angles α_(AC) andα_(BD) as the angle α, or may estimate the angle α by averaging theangles estimated on the basis of differences between phases of three ormore antenna arrays in the X axis direction. In other words, thereceiver may estimate the angle α on the basis of a difference in phasesof at least one antenna array in the X axis direction. In a similar way,the receiver may estimate the angle β on the basis of a difference inphases of at least one antenna array in the Y axis direction.

(3) Coordinate Estimation

The control section 230 performs a coordinate estimation process. Thecoordinate estimation process is a process of estimatingthree-dimensional coordinates (x, y, z) of the portable device 100illustrated in FIG. 4. As the coordinate estimation process, a firstcalculation method and a second calculation method listed below may beadopted.

First Calculation Method

The first calculation method is a method of calculating the coordinatesx, y, and z on the basis of results of the ranging process and the angleestimation process. In this case, the control section 230 firstcalculates the coordinates x and y by using equations listed below.

x=R·cos α

y=R·cos β  (6)

Here, the distance R, the coordinate x, the coordinate y, and thecoordinate z have a relation represented by an equation listed below.

R=√{square root over (x ² +y ² +z ²)}  (7)

The control section 230 calculates the coordinate z by using theabove-described relation and an equation listed below.

z=√{square root over (R ² −R ²·cos² α−R·cos² β)}  (8)

Second Calculation Method

The second calculation method is a method of calculating the coordinatesx, y, and z while omitting estimation of the angles α and β. First, theabove-listed equations (4), (5), (6), and (7) establish a relationrepresented by equations listed below.

x/R=cos α  (9)

y/R=cos β  (10)

x ² +Y ² +Z ² =R ²  (11)

D·cos α=λ·(Pd _(AC)/2+Pd _(BD)/2)/(2·π)  (12)

d·cos β=λ·(Pd _(DC)/2+Pd _(BA)/2)/(2·π)  (13)

The equation (12) is rearranged for cos a, and cos a is substituted intothe equation (9). This makes it possible to obtain the coordinate x byusing an equation listed below.

x=R·λ·(Pd _(AC)/2+Pd _(BD)/2)/(2·π·d)  (14)

The equation (13) is rearranged for cos β, and cos β is substituted intothe equation (10). This makes it possible to obtain the coordinate y byusing an equation listed below.

y=R·λ·(Pd _(DC)/2+Pd _(BA)/2)/(2·π·d)  (15)

Next, the equation (14) and the equation (15) are substituted into theequation (11), and the equation (11) is rearranged. This makes itpossible to obtain the coordinate z by using an equation listed below.

z=√{square root over (R ² −x ² −y ²)}  (16)

The process of estimating the coordinates of the portable device 100 inthe local coordinate system has been described above. It is possible toestimate coordinates of the portable device 100 in the global coordinatesystem by combining the coordinates of the portable device 100 in thelocal coordinate system and coordinates of the origin in the localcoordinate system relative to the global coordinate system.

Cause of Reduction in Accuracy of Estimation

As described above, the coordinates are calculated on the basis of thepropagation delay time and phases. In addition, they are estimated onthe basis of the first incoming waves. Therefore, accuracy of estimatingthe coordinates may deteriorate in a way similar to the ranging processand the angle estimation process.

(4) Estimation of Existence Region

The positional parameters may include a region including the portabledevice 100 among a plurality of predefined regions. For example, in thecase where the region is defined by a distance from the communicationunit 200, the control section 230 estimates the region including theportable device 100 on the basis of the distance R estimated through theranging process. For another example, in the case where the region isdefined by an angle with respect to the communication unit 200, thecontrol section 230 estimates the region including the portable device100 on the basis of the angles α and β estimated through the angleestimation process. For another example, in the case where the region isdefined by the three-dimensional coordinates, the control section 230estimates the region including the portable device 100 on the basis ofthe coordinates (x, y, z) estimated through the coordinate estimationprocess.

Alternatively, in a process specific to the vehicle 202, the controlsection 230 may estimate the region including the portable device 100among the plurality of regions including the vehicle interior and thevehicle exterior of the vehicle 202. This makes it possible to providecourteous service such as providing different serves in the case wherethe user is in the vehicle interior and in the case where the user is inthe vehicle exterior. In addition, the control section 230 may estimatethe region including the portable device 100 among nearby regions andfaraway regions. The nearby regions are regions within a predetermineddistance from the vehicle 202, and the faraway region are thepredetermined distance or more away from the vehicle 202.

(5) Use Pf Result of Estimating Positional Parameter

For example, a result of estimating the positional parameter may be usedfor authentication of the portable device 100. For example, the controlsection 230 determines that the authentication is successful and unlocka door in the case where the portable device 100 is in an area close tothe communication unit 200 on a driver seat side.

3. Technical Problem

Detection of the direct waves as the first incoming waves is not alwayssuccessful with regard to all the wireless communication sections 210.The accuracy of estimating the angle deteriorates in the case wheredetection of the direct waves as the first incoming waves ends infailure with regard to at least any of the plurality of wirelesscommunication sections 210. In addition, the accuracy of estimating theangle deteriorates in the case where the master fails to detect thedirect wave as the first incoming wave. As described above, the accuracyof estimating the positional parameter deteriorate in the case where thedetection of the direct waves as the first incoming waves ends infailure.

Therefore, according to the present invention, there is provided amechanism of estimating an angle on the basis of the first incoming wavedetected by a wireless communication section 210 that is likely tosucceed in detection of the direct wave as the first incoming wave amongthe plurality of wireless communication sections 210. Such aconfiguration makes it possible to improve the accuracy of estimating anangle.

4. Technical Features

(1) Position Estimation Communication

The communication unit 200 according to the present embodiment performsposition estimation communication. The position estimation communicationis communication performed to estimate the positional parameter.Specifically, the position estimation communication includestransmission/reception of the ranging signal and the angle estimationsignal between the portable device 100 and the communication unit 200.

Here, the plurality of wireless communication sections 210 of thecommunication unit 200 are classified into the master and the pluralityof slaves. The master is an example of the first wireless communicationsection 210, which is one of the plurality of wireless communicationsections 210. The slaves are an example of the second wirelesscommunication sections 210, which are wireless communication sections210 other than the first wireless communication section 210 among theplurality of wireless communication sections 210.

With regard to the position estimation communication according to thepresent embodiment, not only the master but also the slaves also receivethe ranging signal. Details thereof will be described with reference toFIG. 9.

FIG. 9 is a sequence diagram for describing an example of the positionestimation communication performed in the system 1 according to thepresent embodiment. The portable device 100 and the communication unit200 are involved in this sequence. It is assumed that the wirelesscommunication section 210A functions as the master in this sequence.

As illustrated in FIG. 9, the portable device 100 first transmits thefirst ranging signal including a pulse (Step S302). Each of the wirelesscommunication section 210A to the wireless communication section 210Dreceives the first ranging signal.

Next, the wireless communication section 210A that has received thefirst ranging signal transmits the second ranging signal including apulse in response to the first ranging signal (Step S304). The portabledevice 100 receives the second ranging signal. In addition, the secondranging signal is also received by each of the plurality of wirelesscommunication sections 210 (wireless communication sections 210B to210D), which are wireless communication sections 210 other than thewireless communication section 210A among the plurality of wirelesscommunication sections 210.

Next, the portable device 100 that has received the second rangingsignal transmits the third ranging signal including a pulse in responseto the second ranging signal (Step S306). Each of the wirelesscommunication section 210A to the wireless communication section 210Dreceives the third ranging signal.

The portable device 100 measures time T₁ from transmission time of thefirst ranging signal to reception time of the second ranging signal, andtime T₂ from reception time of the second ranging signal to transmissiontime of the third ranging signal. Here, the reception time of the secondranging signal is reception time of the first incoming wave of thesecond ranging signal, that is, time corresponding to a specific elementin a CIR calculated with regard to the second ranging signal. Next, theportable device 100 transmits a signal including information indicatingthe time T₁ and the time T₂ (Step S308). Such a signal is received byeach of the plurality of wireless communication sections 210.

In this sequence, the third ranging signal also serve as the angleestimation signal. Alternatively, the first ranging signal may alsoserve as the angle estimation signal.

(2) Specific Element Detection Process

The control section 230 acquires a plurality of e pieces ofchronological information including, as the elements related to time,information that chronologically changes and that is obtained when theplurality of wireless communication sections receive the ranging signaltransmitted from the portable device 100. The ranging signal is anexample of the pulse signal that is a signal including a pulse. Forexample, the chronological information is a CIR including a CIR valuethat chronologically changes, as an element related to time. Forexample, the control section 230 calculates respective CIRs with regardto the plurality of wireless communication sections 210 including themaster and the slaves, on the basis of the respective ranging signalsreceived by the plurality of wireless communication sections 210.

Next, the control section 230 performs a specific element detectionprocess of detecting specific elements of the CIRs based on therespective ranging signal received by the plurality of wirelesscommunication sections 210, on the basis of the respective CIRs acquiredwith regard to the plurality of wireless communication sections 210.Specifically, the control section 230 detects the respective specificelements with regard to the plurality of wireless communication sections210, from the respective CIRs obtained when the plurality of wirelesscommunication sections 210 receive the third ranging signal that alsoserves as the angle estimation signal as illustrated in FIG. 9. Thespecific element detection process is an example of a first process.

The control section 230 detects the specific elements in accordance witha predetermined standard. For example, the control section 230 detectsthe specific elements in accordance with a predetermined standard bydetecting, as the specific elements, one or more elements whoseamplitude component included in the CIR value exceeds a predeterminedthreshold. The amplitude component included in the CIR value may beamplitude itself or electric power obtained by squaring the amplitude.

The specific element is an element corresponding to the first incomingwave. In other words, the detection of the specific element issynonymous with the above-described detection of the first incomingwave. In addition, the detection of the direct wave as the firstincoming wave is synonymous with detection of the specific elementcorresponding to the direct wave.

Time corresponding to delay time of the specific element serves as timeof receiving the first incoming wave and is used for ranging. Inaddition, the phase of the specific element serves as the phase of thefirst incoming wave and is used for angle estimation. In other words,the control section 230 detects the specific element to be used for thepositional parameter estimation with regard to the plurality of wirelesscommunication sections 210.

For example, the control section 230 detects the specific elements inaccordance with the predetermined standard by detecting elements whoseamplitude component included in the CIR value exceeds a first thresholdfor the first time. In this case, the specific elements are detected oneby one with regard to the plurality of CIRs obtained with regard to theplurality of wireless communication sections 210. The predeterminedthreshold is the above-described first path threshold. In other words,the specific element is an element whose amplitude component included inthe CIR value exceeds the first path threshold for the first time, amongthe plurality of elements of the CIRs. This makes it possible to reducecomputational load for detecting the specific elements in comparisonwith the case of detecting the plurality of specific elements from asingle CIR.

Therefore, in the specific element detection process, the respectivespecific elements are detected one by one with regard to the pluralityof wireless communication sections 210.

(3) Verification Process

The control section 230 performs a verification process of verifyingwhether each of the plurality of specific elements detected through thespecific element detection process is based on the ranging signal comingthrough a shortest path from the portable device 100 to each of theplurality of wireless communication sections 210. The case where thespecific element is based on the ranging signal coming through theshortest path (that is, first path) from the portable device 100 to thewireless communication section 210 means that the specific elementcorresponds to the direct wave. In other words, the control section 230verifies whether or not each of the plurality of specific elementsdetected with regard to the plurality of wireless communication sections210 corresponds to the direct wave. The verification process is anexample of a second process.

The control section 230 calculates an indicator that indicates apossibility that each of the plurality of specific elements detectedthrough the specific element detection process is based on the rangingsignal coming through the first path. In other words, the controlsection 230 calculates the indicator that indicates a possibility thateach of the plurality of specific elements detected through the specificelement detection process corresponds to the direct wave. Hereinafter,such an indicator is also referred to as a first path indicator.

The first path indicators are continuous values or discrete values, forexample. For example, the first path indicator having a smaller valuemay indicate a higher possibility that the specific element correspondsto the direct wave. In a similar way, the first path indicator having alarger value may indicate a lower possibility that the specific elementcorresponds to the direct wave, and vice versa.

In addition, in the verification process, the control section 230verifies whether or not each of the plurality of specific elements isbased on the ranging signal coming through the first path, on the basisof the first path indicator calculated with regard to each of theplurality of specific elements. In other words, the control section 230verifies whether or not each of the plurality of specific elementscorresponds to the direct wave, on the basis of the first pathindicator.

First First Path Indicator

The first path indicator may be the ranging value estimated with regardto each of the plurality of wireless communication sections 210. Such afirst path indicator is also referred to as a first first pathindicator.

The ranging value is a distance between the portable device 100 and thewireless communication section 210. The distance is estimated on thebasis of the propagation delay time. The propagation delay time is timefrom transmission to reception of the ranging signal between theportable device 100 and the wireless communication section 210. Thepropagation delay time is calculated on the basis of the specificelements. Hereinafter, details of a process of calculating therespective ranging value with regard to the plurality of wirelesscommunication sections 210 will be described.

Master

As illustrated in FIG. 9, the control section 230 measures time T_(3-m)from time of reception of the first ranging signal to time oftransmission of the second ranging signal. Specifically, the controlsection 230 measures the time T_(3-m) from time corresponding to thespecific element of the CIR obtained when the master receives the firstranging signal to time at which the master transmits the second rangingsignal. The time T_(3-m) corresponds to the time T₃ described withregard to the ranging process.

In addition, as illustrated in FIG. 9, the control section 230 measurestime T₄ from time of transmission of the second ranging signal to timeof reception of the first incoming wave of the third ranging signal.Specifically, the control section 230 measures the time T_(4-m) fromtime at which the master transmits the second ranging signal to timecorresponding to the specific element of the CIR obtained when themaster receives the third ranging signal. The time T_(4-m) correspondsto the time T₄ described with regard to the ranging process.

Next, the control section 230 acquires a ranging value between theportable device 100 and the master on the basis of the time T₁ and thetime T₂ measured by the portable device 100, and the time T_(3-m) andthe time T_(4-m) measured with regard to the master. Specifically, thecontrol section 230 estimates the propagation delay time τ_(m) by usingan equation listed below. Next, the control section 230 acquires theranging value on the basis of the propagation delay time τ_(m). Notethat, as illustrated in FIG. 9 the portable device 100 notifies of thetime T₁ and the time T₂.

$\begin{matrix}{\tau_{m} = \frac{{T_{1} \times T_{4 - m}} - {T_{2} \times T_{3 - m}}}{T_{1} + T_{2} + T_{3 - m} + T_{4 - m}}} & (17)\end{matrix}$

Slave

Because the master transmits the second ranging signal, it is difficultfor the slave to acquire transmission time of the second ranging signal.Therefore, the control section 230 uses reception time of the firstincoming wave of the second ranging signal transmitted from the master,instead of the transmission time of the second ranging signal, withregard to the slave.

First, as illustrated in FIG. 9, the control section 230 measures timeT_(3-s) (T_(3-s1), T_(3-s2), and T_(3-s3)) from reception time of thefirst incoming wave of the first ranging signal to reception time of thefirst incoming wave of the second ranging signal.

Specifically, the control section 230 measures the time T_(3-s) fromtime corresponding to the specific element of the CIR obtained when theslave receives the first ranging signal to time corresponding to thespecific element of the CIR obtained when the slave receives the secondranging signal.

Next, as illustrated in FIG. 9, the control section 230 measures timeT_(4-s) (T_(4-s1), T_(4-s2), and T_(4-s3)) from reception time of thefirst incoming wave of the second ranging signal to reception time ofthe first incoming wave of the third ranging signal. Specifically, thecontrol section 230 measures the time T_(4-s) from time corresponding tothe specific element of the CIR obtained when the slave receives thesecond ranging signal to time corresponding to the specific element ofthe CIR obtained when the slave receives the third ranging signal.

Next, the control section 230 acquires a ranging value between theportable device 100 and the slave on the basis of the time T₁ and thetime T₂ measured by the portable device 100, and the time T_(3-s) andthe time T_(4-s) measured with regard to the slave. For example, thecontrol section 230 estimates propagation delay times τ_(s) (τ_(s1),τ_(s2), and τ_(s3)) with regard to each of the plurality of slaves byusing an equation listed below. Next, the control section 230 acquires aranging value with regard to each of the plurality of slaves on thebasis of the propagation delay times is with regard to each of theplurality of slaves. Note that, as illustrated in FIG. 9 the portabledevice 100 notifies of the time T₁ and the time T₂.

$\begin{matrix}{\tau_{s} = \frac{{T_{1} \times T_{4 - s}} - {T_{2} \times T_{3 - s}}}{T_{1} + T_{2} + T_{3 - s} + T_{4 - s}}} & (18)\end{matrix}$

Note that, by using the above-listed equation, the ranging value of thewireless communication section 210B is acquired on the basis of τ_(s1)obtained by substituting T_(3-s1) into the above-listed equation asT_(3-s), and substituting T_(4-s1) as T_(4-s). In a similar way, byusing the above-listed equation, the ranging value of the wirelesscommunication section 210C is acquired on the basis of τ_(s2) obtainedby substituting T_(3-s2) into the above-listed equation as T_(3-s), andsubstituting T_(4-s2) as T_(4-s). In a similar way, by using theabove-listed equation, the ranging value of the wireless communicationsection 210D is acquired on the basis of τ_(s3) obtained by substitutingT_(3-s3) into the above-listed equation as T_(3-s), and substitutingT_(4-s3) as T_(4-s).

Relation Between Ranging Value of Master and Ranging Value of Slave

A distance between adjacent wireless communication sections 210 is anultrashort distance that is half or less of wavelength X of a carrierwave of the angle estimation signal.

Therefore, distances to the portable device 100 can be considered to bethe same with regard to all the wireless communication sections 210.Therefore, starts of T_(3-m), T_(3-s1), T_(3-s2), and T_(3-s3) are thesame or substantially the same in the case where detection of thespecific elements corresponding to the direct waves of the first rangingsignals is successful with regard to all the wireless communicationsections 210. In a similar way, ends of T_(4-m), T_(4-s1), T_(4-s2), andT_(4-s3) are the same or substantially the same in the case wheredetection of the specific elements corresponding to the direct waves ofthe third ranging signals is successful with regard to all the wirelesscommunication sections 210.

In addition, for a similar reason, it is possible to consider that thetransmission time of the second ranging signal of the master issubstantially the same as the reception time of the first incoming waveof the second ranging signal of the slave, if it is assumed that noobstacle is interposed between the master and the slave. In other words,the ends of T_(3-m), T_(3-s1), T_(3-s2), and T_(3-s3) are substantiallythe same. In addition, the starts of T_(4-m), T_(4-s1), T_(4-s2), andT_(4-s3) are substantially the same.

As described above, T_(3-m), T_(3-s1), T_(3-s2), and T_(3-s3) are thesame or substantially the same in the case where detection of thespecific elements corresponding to the direct waves of the first rangingsignals is successful with regard to all the wireless communicationsections 210. In addition, T_(4-m), T_(4-s1), T_(4-s2), and T_(4-s3) arethe same or substantially the same in the case where detection of thespecific elements corresponding to the direct waves of the third rangingsignals is successful with regard to all the wireless communicationsections 210.

Therefore, the ranging values are substantially the same with regard toall the wireless communication sections 210, in the case where detectionof the specific elements corresponding to the direct waves is successfulwith regard to all the wireless communication sections 210.

Verification of Whether or not Specific Element Corresponds to DirectWave

As described above about the ranging process, the ranging value isestimated as a distance longer than the true value in the case where thedirect wave is not detected as the first incoming wave, that is, in thecase where the specific element does not correspond to the direct wave.In other words, it can be said that, as the ranging value is smaller,there is a higher possibility that the specific element used forcalculation of the ranging value corresponds to the direct wave. On theother hand, it can be said that, as the ranging value is larger, thereis a higher possibility that the specific element used for calculationof the ranging value does not correspond to the direct wave.

Accordingly, in the verification process, the control section 230verifies that, among the plurality of ranging values estimated withregard to the respective specific elements, the specific element fromwhich the ranging value whose difference from the shortest ranging valueis the first threshold or less is estimated is based on the rangingsignal coming through the first path. In other words, the controlsection 230 determines that, among the ranging values estimated on thebasis of the respective specific elements detected with regard to theplurality of wireless communication sections 210, the specific elementfrom which the ranging value whose difference from the shortest rangingvalue is the first threshold or less is estimated corresponds to thedirect wave. On the other hand, the control section 230 determines that,among the ranging values estimated on the basis of the respectivespecific elements detected with regard to the plurality of wirelesscommunication sections 210, the specific element from which the rangingvalue whose difference from the shortest ranging value exceeds the firstthreshold is estimated does not correspond to the direct wave.

As described above, by using the first first path indicator, it ispossible to verify whether or not the specific element corresponds tothe direct wave from a viewpoint of the ranging value.

(4) Signal Arrival Angle Estimation Process

The control section 230 performs a signal arrival angle estimationprocess on the basis of a plurality of specific elements verified aselements based on the ranging signals coming through the first path,among the specific elements of the CIRs based on the respective rangingsignals received by the plurality of wireless communication sections210. The signal arrival angle estimation process is a process ofestimating a ranging signal arrival angle (hereinafter, also referred toas a signal arrival angle) by using axes extending from reference point,which is set to the plurality of wireless communication sections 210, asreference axes. Specifically, the control section 230 estimates thesignal arrival angle on the basis of the plurality of specific elementsverified as elements corresponding to the direct waves by using thefirst path indicator, among the plurality of specific elements detectedfrom the CIRs obtained when the plurality of wireless communicationsections 210 receive the respective third ranging signals serving as theangle estimation signals as illustrated in FIG. 9.

For example, the reference point is the origin of the local coordinatesystem of the communication unit 200. For example, the reference axis isa coordinate axis of the local coordinate system of the communicationunit 200. In addition, for example the signal arrival angles are theangles α and β described above about the angle estimation process. Inthis case, the signal arrival angle estimation process is similar to theprocess of estimating the angles α and β in the angle estimationprocess. In other words, the signal arrival angle corresponds to anangle of the portable device 100 with respect to the communication unit200. The angle of the portable device 100 is one of the positionalparameters of the portable device 100.

Specifically, in the signal arrival angle estimation process, thecontrol section 230 estimates the signal arrival angle on the basis of aphase component included in the CIR value of the specific elementverified as the element based on the ranging signal coming through thefirst path. For example, the control section 230 estimates the angle αwith respect to the X axis, while using a difference between phasecomponents of specific elements of the pair of the wirelesscommunication sections 210 forming the antenna array in the X axisdirection, as the antenna array phase difference in the X axisdirection. In addition, the control section 230 estimates the angle βwith respect to the Y axis, while using a difference between phasecomponents of specific elements of the pair of the wirelesscommunication sections 210 forming the antenna array in the Y axisdirection, as the antenna array phase difference in the Y axisdirection. As described above about the angle estimation process, it ispossible to improve accuracy of estimating the signal arrival angle byestimating the angle on the basis of the phase component of the specificelement verified as the element corresponding to the direct wave. Thesignal arrival angle estimation process is an example of a thirdprocess.

Here, as described above about the angle estimation process, it ispossible for the receiver to estimate the angle α on the basis of adifference in phases of at least one antenna array in the X axisdirection. In addition, it is possible for the receiver to estimate theangle β on the basis of a difference in phases of at least one antennaarray in the Y axis direction. The wireless communication sections 210forming the antenna array in the X axis direction may partially overlapthe wireless communication sections 210 forming the antenna array in theY axis direction. For example, it is possible to estimate the angle αand the angle β on the basis of a difference in phases of the antennaarray including the wireless communication section 210A and the wirelesscommunication section 210C in the X axis direction, and a difference inphases of the antenna array including the wireless communication section210A and the wireless communication section 210B in the Y axisdirection. Accordingly, the receiver can estimate the angle α and theangle β on the basis of the specific elements of at least three wirelesscommunication sections 210.

Therefore, the control section 230 extracts the respective phasecomponents included in the three or more specific elements that areverified as the specific elements based on the ranging signals comingthrough the first path, and estimates the signal arrival angles on thebasis of the three or more phase components that have been extracted. Inother words, the control section 230 estimates the signal arrival angleon the basis of the three or more specific elements verified as thespecific elements corresponding to the direct wave by using the firstpath indicator. The control section 230 can reduce processing load bylimiting the number of specific elements to be used for estimating thesignal arrival angle to three. On the other hand, the control section230 can improve accuracy of estimating the signal arrival angle by usingfour or more specific elements for estimating the signal arrival angle.

Here, the three or more specific elements used for estimating the signalarrival angle is preferably specific elements detected with regard tothree or more wireless communication sections 210 that form a plane. Inother words, the control section 230 preferably estimates the signalarrival angle on the basis of the respective phase components includedin the three or more specific elements detected with regard to the threeor more wireless communication sections 210 that form a plane.

In the case where the three or more wireless communication sections 210forms a plane, the three or more wireless communication sections 210 arenot disposed on a same straight line. This makes it possible to estimatethe signal arrival angles with respect to the two reference axes such asthe angle α with respect to the X axis and the angle β with respect tothe Y axis.

(5) Flow of Process

FIG. 10 is a flowchart illustrating an example of a flow of a processexecuted by the communication unit 200 according to the presentembodiment.

As illustrated in FIG. 10, the communication unit 200 first performs theposition estimation communication with the portable device 100 (StepS402). The details of the position estimation communication have beendescribed above with reference to FIG. 9.

Next, the control section 230 detects the respective specific elementswith regard to the plurality of wireless communication sections 210(Step S404). Specifically, the control section 230 detects therespective specific elements from the respective CIRs obtained when theplurality of wireless communication sections 210 receive the respectiveranging signals through the position estimation communication.

Next, the control section 230 calculates the respective ranging valueswith regard to the plurality of wireless communication sections 210(Step S406). Specifically, the control section 230 first calculates thepropagation delay time on the basis of time corresponding to thespecific element detected with regard to each of the plurality ofwireless communication sections 210. Next, the control section 230calculates the ranging value between the portable device 100 and each ofthe plurality of wireless communication sections 210, on the basis ofthe propagation delay time calculated with regard to each of theplurality of wireless communication sections 210.

Next, the control section 230 decides a threshold (Step S408). Forexample, the control section 230 decides the threshold by using anequation listed below.

TH=min(R _(m) ,R _(s1) ,R _(s2) ,R _(s3))+α  (19)

Here, TH represents the decided threshold. R_(m) is a ranging value ofthe master. R_(s1), R_(s2), and R_(s3) are ranging values of therespective slaves. α is a predetermined value. The ranging value whosedifference from a shortest ranging value is a or less is verified as avalue corresponding to the direct wave. In other words, a is an exampleof the first threshold.

Next, the control section 230 determines whether the number of wirelesscommunication sections 210 whose ranging values are the threshold orless is three or more (Step S410).

The process returns to Step S402 again in the case where it isdetermined that the number of wireless communication sections 210 whoseranging values are the threshold or less is not three or more (NO inStep S410).

On the other hand, in the case where it is determined that the number ofwireless communication sections 210 whose ranging values are thethreshold or less is three or more (YES in Step S410), the controlsection 230 estimates the signal arrival angle on the basis of the phasecomponents of the specific elements obtained with regard to the wirelesscommunication sections 210 whose ranging values are the threshold orless (Step S412). Specifically, the control section 230 first calculatesthe antenna array phase difference with regard to at least two referenceaxes on the basis of the phase components of the specific elementsdetected with regard to the three or more wireless communicationsections 210 that form a plane. In addition, the control section 230estimates the signal arrival angles with respect to the at least tworeference axes on the basis of the antenna array phase difference withregard to the at least two reference axes.

(6) Another Example of First Path Indicator

Various kinds of first path indicators can be used instead of theabove-described ranging values. Next, another example of the first pathindicator will be described.

Second First Path Indicator

The first path indicator may be the propagation delay time calculatedwith regard to each of the plurality of wireless communication sections210. Such a first path indicator is also referred to as a second firstpath indicator.

The propagation delay time is a time period from transmission toreception of the ranging signal between the portable device 100 and thewireless communication section 210 as described above about the firstfirst path indicator. The propagation delay time is calculated on thebasis of the specific elements.

As described above about the ranging process, the propagation delay timeobtained in the case where the direct wave is not detected as the firstincoming wave is longer than the propagation delay time obtained in thecase where the direct wave is detected as the first incoming wave. Inother words, it can be said that, as the propagation delay time isshorter, there is a higher possibility that the specific element usedfor calculation of the propagation delay time corresponds to the directwave. On the other hand, it can be said that, as the propagation delaytime is longer, there is a higher possibility that the specific elementused for calculation of the propagation delay time does not correspondto the direct wave.

Therefore, in the verification process, the control section 230 verifiesthat, among the plurality of propagation delay times calculated withregard to the respective specific elements, the specific element fromwhich the propagation delay time whose difference from the shortestpropagation delay time is the second threshold or less is calculated isbased on the ranging signal coming through the first path. In otherwords, the control section 230 determines that, among the propagationdelay times calculated on the basis of the respective specific elementsdetected with regard to the plurality of wireless communication sections210, the specific element from which the propagation delay time whosedifference from the shortest propagation delay time is the secondthreshold or less is calculated corresponds to the direct wave. On theother hand, the control section 230 determines that, among thepropagation delay times calculated on the basis of the respectivespecific elements detected with regard to the plurality of wirelesscommunication sections 210, the specific element from which thepropagation delay time whose difference from the shortest propagationdelay time exceeds the second threshold is calculated does notcorrespond to the direct wave.

As described above, by using the second first path indicator, it ispossible to verify whether or not the specific element corresponds tothe direct wave from a viewpoint of the propagation delay time.

Third First Path Indicator

The first path indicator may be the time T₃ calculated with regard toeach of the plurality of wireless communication sections 210. Such afirst path indicator is also referred to as a third first pathindicator.

The third first path indicator related to the master is the timeT_(3-m). As described above, the time T_(3-m) is a time period from timecorresponding to the specific element of the CIR obtained when themaster receives the first ranging signal (which is an example of thefirst signal) to time at which the master transmits the second rangingsignal (which is an example of the second signal).

The third first path indicator related to the slave is the time T_(3-s)(T_(3-s1), T_(3-s2), and T_(3-s3)). As described above, the time T_(3-s)is a time period from time corresponding to the specific element of theCIR obtained when the slave receives the first ranging signal to timecorresponding to the specific element of the CIR obtained when the slavereceives the second ranging signal.

As described above about the ranging process, the reception time of thefirst incoming wave is delayed in the case where the direct wave is notdetected as the first incoming wave. In other words, the timecorresponding to the specific element is delayed in the case where thedirect wave is not detected as the first incoming wave. Therefore, inthe case where the direct wave is not detected as the first incomingwave, the time corresponding to the specific element of the firstranging signal of each of the plurality of wireless communicationsections 210 is delayed.

This time serves as a start of the time T₃ (T_(3-m), T_(3-s1), T_(3-s2),or T_(3-s3)). On the other hand, as described above about the firstfirst path indicator, ends of T_(3-m), T_(3-s1), T_(3-s2), and T_(3-s3)are substantially the same if it is assumed that no obstacle isinterposed between the master and the slaves. Accordingly, in the casewhere the direct wave is not detected as the first incoming wave,shorter time T₃ is obtained in comparison with the case where the directwave is detected as the first incoming wave.

Therefore, in the verification process, the control section 230 verifiesthat the specific element detected with regard to the wirelesscommunication section 210 whose calculated difference from longest timeis a third threshold or less is based on the ranging signal comingthrough the first path, among time T_(3-m) serving as the third firstpath indicator related to the master and times T_(3-s) serving as therespective third first path indicators related to of the plurality ofslaves. Accordingly, the control section 230 determines that thespecific element from which time whose difference from longest time isthe third threshold or less is calculated corresponds to the directwave, among the times T_(3-m), T_(3-s1), T_(3-s2), and T_(3-s3). On theother hand, the control section 230 determines that the specific elementfrom which time whose difference from the longest time exceeds the thirdthreshold is calculated does not correspond to the direct wave, amongthe times T_(3-m), T_(3-s1), T_(3-s2), and T_(3-s3).

As described above, by using the third first path indicator, it ispossible to verify whether or not the specific element corresponds tothe direct wave from a viewpoint of the time T₃.

Fourth First Path Indicator

The first path indicator may be the time T₄ calculated with regard toeach of the plurality of wireless communication sections 210.Hereinafter, such a first path indicator is also referred to as a fourthfirst path indicator.

The fourth first path indicator related to the master is time T_(4-m).As described above, the time T_(4-m) is a time period from time at whichthe master transmits the second ranging signal to time corresponding tothe specific element of the CIR obtained when the master receives thethird ranging signal (which is an example of the third signal).

The fourth first path indicator related to the slave is the time T_(4-s)(T_(4-s1), T_(4-s2), and T_(4-s3)). As described above, the time T_(4-s)is a time period from time corresponding to the specific element of theCIR obtained when the slave receives the second ranging signal to timecorresponding to the specific element of the CIR obtained when the slavereceives the third ranging signal.

As described above about the ranging process, the reception time of thefirst incoming wave is delayed in the case where the direct wave is notdetected as the first incoming wave. In other words, the timecorresponding to the specific element is delayed in the case where thedirect wave is not detected as the first incoming wave. Therefore, inthe case where the direct wave is not detected as the first incomingwave, the time corresponding to the specific element of the thirdranging signal of each of the plurality of wireless communicationsections 210 is delayed. This time serves as an end of the time T₄(T_(4-m), T_(4-s1), T_(4-s2), or T_(4-s3)). On the other hand, asdescribed above about the first first path indicator, starts of T_(4-m),T_(4-s1), T_(4-s2), and T_(4-s3) are substantially the same if it isassumed that no obstacle is interposed between the master and theslaves. Accordingly, in the case where the direct wave is not detectedas the first incoming wave, longer time T₄ is obtained in comparisonwith the case where the direct wave is detected as the first incomingwave.

Therefore, in the verification process, the control section 230 verifiesthat the specific element detected with regard to the wirelesscommunication section 210 whose calculated difference from shortest timeis a fourth threshold or less is based on the ranging signal comingthrough the first path, among time T_(4-m) serving as the fourth firstpath indicator related to the master and times T_(4-s) serving as therespective fourth first path indicators related to of the plurality ofslaves. Accordingly, the control section 230 determines that thespecific element from which time whose difference from shortest time isthe fourth threshold or less is calculated corresponds to the directwave, among the times T_(4-m), T_(4-s1), T_(4-s2), and T_(4-s3). On theother hand, the control section 230 determines that the specific elementfrom which time whose difference from the shortest time exceeds thefourth threshold is calculated does not correspond to the direct wave,among the times T_(4-m), T_(4-s1), T_(4-s2), and T_(4-s3).

As described above, by using the fourth first path indicator, it ispossible to verify whether or not the specific element corresponds tothe direct wave from a viewpoint of the time T₄.

Fifth First Path Indicator

The first path indicator may be time corresponding to the specificelement with regard to each of the plurality of wireless communicationsections 210. Hereinafter, such a first path indicator is also referredto as a fifth first path indicator.

Specifically, the fifth first path indicator is time corresponding tothe specific element of the CIR obtained when the wireless communicationsection 210 receives the ranging signal. In particular, the fifth firstpath indicator is time corresponding to the specific element of the CIRobtained when each of the plurality of wireless communication sections210 receives a same ranging signal. Here, the ranging signal is thefirst ranging signal or the third ranging signal.

As described above about the ranging process, the reception time of thefirst incoming wave is delayed in the case where the direct wave is notdetected as the first incoming wave. In other words, the timecorresponding to the specific element is delayed in the case where thedirect wave is not detected as the first incoming wave.

Therefore, in the verification process, the control section 230 verifiesthat, among times corresponding to the respective specific elements ofthe plurality of wireless communication sections 210, the specificelement corresponding to time whose difference from earliest time is afifth threshold or less is based on the ranging signal coming throughthe first path. In other words, the control section 230 determines that,among the specific elements, a specific element corresponding to timewhose difference from earliest time is the fifth threshold or lesscorresponds to the direct wave. On the other hand, the control section230 determines that, among the specific elements, the specific elementcorresponding to time whose difference from earliest time exceeds thefifth threshold does not correspond to the direct wave.

As described above, by using the fifth first path indicator, it ispossible to verify whether or not the specific element corresponds tothe direct wave from a viewpoint of time corresponding to the specificelement.

5. Supplement

Heretofore, preferred embodiments of the present invention have beendescribed in detail with reference to the appended drawings, but thepresent invention is not limited thereto. It should be understood bythose skilled in the art that various changes and alterations may bemade without departing from the spirit and scope of the appended claims.

For example, in the above-described embodiments, reception times of thefirst incoming waves of the second ranging signals transmitted from themaster are used as the end of the time T_(3-s) with regard to the slaveand the start of the time T_(4-s) with regard to the slave. However, thepresent invention is not limited thereto. For example, the controlsection 230 may use the transmission times of the second ranging signalswith regard to the master, as the end of the time T_(3-s) with regard tothe slave and the start of the time T_(4-s) with regard to the slave.

For example, the above embodiment has been described on the assumptionthat the communication unit 200 includes the four wireless communicationsections 210. However, present invention is not limited thereto. It issufficient for the communication unit 200 to include at least threewireless communication sections 210. Alternatively, the communicationunit 200 may include the five or more wireless communication sections210.

For example, it is also possible to use a combination of any two or morefirst path indicators among the plurality of first path indicatorsdescribed in the above embodiment.

For example, in the above-described embodiment, the specific element isan element whose CIR value exceeds the first path threshold for thefirst time.

However, the present invention is not limited thereto. For example, thespecific element may be an element whose CIR value exceeds the firstpath threshold for the second or subsequent time.

For example, the above embodiment has been described on the assumptionthat the CIR is the correlation computation result. However, presentinvention is not limited thereto. For example, the CIR may be areception signal itself. In this case, the CIR includes a resultobtained by sampling the pulse received by the wireless communicationsection 210 at designated intervals, as the element obtained at eachtiming between the designated intervals. The CIR value is the receptionsignal received at each delay time. Here, it is sufficient for the CIRvalue to include at least any of the amplitude component and the phasecomponent of the reception signal. The amplitude component of thereception signal is amplitude or electric power obtained by squaring theamplitude. The phase component of the reception signal is an anglebetween IQ components of the reception signal and an I axis on an IQplane. The phase component may be simply referred to as a phase. Thereception signal may be a complex number including the IQ components. Inthe case where the CIR is the reception signal itself, the receiver mayuse a condition that the amplitude of the received wireless signalexceeds the first path threshold for the first time, as thepredetermined detection standard for detecting the first incoming wave.In this case, the receiver may detect an element whose amplitudecomponent of the received wireless signal exceeds the first paththreshold for the first time, as the specific element. In other words,the receiver may detect a portion obtained when the amplitude componentof the reception signal exceeds the first path threshold for the firsttime, as the first incoming wave.

For example, in the above-described embodiment, the control section 230calculates the CIR, detects the first incoming wave (that is, specificelement), and estimates the positional parameter. However, the presentinvention is not limited thereto. Any of the above-described processesmay be performed by the wireless communication section 210. For example,each of the plurality of wireless communication sections 210 maycalculate the CIR and detect the first incoming wave on the basis of thereception signal received by each of the plurality of wirelesscommunication sections 210. In addition, the positional parameter may beestimated by the wireless communication section 210 that functions asthe master.

For example, according to the above-described embodiment, thedescription has been given with reference to the example in which theangles α and β are calculated on the basis of antenna array phasedifferences between antennas in a pair. However, the present inventionis not limited thereto. For example, the communication unit 200 maycalculate the angles α and β through beamforming using the plurality ofantennas 211. In this case, the communication unit 200 scans main lobesof the plurality of antennas 211 in all the directions, determines thatthe portable device 100 exists in a direction with largest receptionelectric power, and calculates the angles α and β on the basis of thisdirection.

For example, according to the above-described embodiment, as describedwith reference to FIG. 3, the local coordinate system has been treatedas a coordinate system including coordinate axes parallel to axesconnecting the antennas in the pairs. However, the present invention isnot limited thereto. For example, the local coordinate system may be acoordinate system including coordinate axes that are not parallel to theaxes connecting the antennas in the pairs. In addition, the origin isnot limited to the center of the plurality antennas 211. The localcoordinate system according to the present embodiment may be arbitrarilyset on the basis of arrangement of the plurality of antennas 211 of thecommunication unit 200.

For example, although the example in which the portable device 100serves as the authenticatee and the communication unit 200 serves as theauthenticator has been described in the above embodiment, the presentinvention is not limited thereto. The roles of the portable device 100and the communication unit 200 may be reversed. For example, thepositional parameter may be estimated by the portable device 100. Inaddition, the roles of the portable device 100 and the communicationunit 200 may be switched dynamically. In addition, a plurality of thecommunication units 200 may determine the positional parameters, andperform authentication.

For example, although the example in which the present invention isapplied to the smart entry system has been described in the aboveembodiment, the present invention is not limited thereto. The presentinvention is applicable to any system that estimates the positionalparameter and performs the authentication by transmitting/receivingsignals. For example, the present invention is applicable to a pair ofany two devices selected from a group including portable devices,vehicles, smartphones, drones, houses, home appliances, and the like. Inthis case, one in the pair operates as the authenticator, and the otherin the pair operates as the authenticatee. Note that, the pair mayinclude two device of a same type, or may include two different types ofdevices. In addition, the present invention is applicable to a casewhere a wireless local area network (LAN) router estimates a position ofa smartphone.

For example, in the above embodiment, the standard using UWB has beenexemplified as the wireless communication standard. However, the presentinvention is not limited thereto. For example, it is also possible touse a standard using infrared as the wireless communication standard.

Note that, a series of processes performed by the devices described inthis specification may be achieved by any of software, hardware, and acombination of software and hardware. A program that configures softwareis stored in advance in, for example, a recording medium (non-transitorymedium) installed inside or outside the devices. In addition, forexample, when a computer executes the programs, the programs are readinto random access memory (RAM), and executed by a processor such as aCPU. The recording medium may be a magnetic disk, an optical disc, amagneto-optical disc, flash memory, or the like. Alternatively, theabove-described computer program may be distributed via a networkwithout using the recording medium, for example.

Further, in the present specification, the processes described usingflowcharts are not necessarily executed in the order illustrated in thedrawings. Some processing steps may be executed in parallel. Inaddition, additional processing steps may be employed and someprocessing steps may be omitted.

REFERENCE SIGNS LIST

-   1 system-   100 portable device-   110 wireless communication section-   111 antenna-   120 storage section-   130 control section-   200 communication unit-   202 vehicle-   210 wireless communication section-   211 antenna-   220 storage section-   230 control section

What is claimed is:
 1. A communication device comprising: a plurality ofwireless communication sections, each of which is configured towirelessly receive a signal from another communication device; and acontrol section configured to perform a first process of detecting aspecific element that is a certain element in chronological informationbased on respective pulse signals received by the plurality of wirelesscommunication sections, on a basis of respective pieces of chronologicalinformation including, as elements related to time, information thatchronologically changes and that is obtained when the plurality ofwireless communication sections receive the respective pulse signals,which are signals including a pulse transmitted from the othercommunication device, perform a second process of verifying whether eachof a plurality of the specific elements detected through the firstprocess is based on the pulse signal coming through a shortest path fromthe other communication device to each of the plurality of wirelesscommunication sections, and perform a third process of estimating anangle from which the pulse signal has come while using axes extendingfrom reference point, which is set to the plurality of wirelesscommunication sections, as reference axes, on a basis of the pluralityof specific elements that are verified as elements based on the pulsesignals coming through the shortest path among the specific elements inthe chronological information based on the respective pulse signalsreceived by the plurality of wireless communication sections.
 2. Thecommunication device according to claim 1, wherein, in the secondprocess, the control section calculates an indicator that indicates apossibility that each of the plurality of specific elements detectedthrough the first process is based on the pulse signal coming throughthe shortest path, and verifies whether or not each of the plurality ofspecific elements is based on the pulse signal coming through theshortest path, on a basis of the indicator calculated with regard toeach of the plurality of specific elements.
 3. The communication deviceaccording to claim 2, wherein the indicator is a ranging value that is adistance between the other communication device and the wirelesscommunication section, which is estimated on a basis of propagationdelay time calculated on a basis of the specific element, thepropagation delay time being time from transmission to reception of thepulse signal between the other communication device and the wirelesscommunication section, and in the second process, the control sectionverifies that, among a plurality of the ranging values estimated withregard to the respective specific elements, the specific element fromwhich the ranging value whose difference from the shortest ranging valueis a first threshold or less is estimated is based on the pulse signalcoming through the shortest path.
 4. The communication device accordingto claim 2, wherein the indicator is propagation delay time that iscalculated on a basis of the specific elements and that is time fromtransmission to reception of the pulse signal between the othercommunication device and the wireless communication section, and in thesecond process, the control section verifies that, among a plurality ofthe propagation delay times calculated with regard to the respectivespecific elements, the specific element from which the propagation delaytime whose difference from the shortest propagation delay time is asecond threshold or less is calculated is based on the pulse signalcoming through the shortest path.
 5. The communication device accordingto claim 2, wherein each of the plurality of wireless communicationsections receives a first signal that is the pulse signal transmittedfrom the other communication device, a first wireless communicationsection, which is one of the plurality of wireless communicationsections, transmits a second signal that is the pulse signal in responseto the first signal, each of a plurality of second wirelesscommunication sections, which are wireless communication sections otherthan the first wireless communication section among the plurality ofwireless communication sections, receives the second signal, theindicator related to the first wireless communication section is aperiod of time from time corresponding to the specific element in thechronological information obtained when the first wireless communicationsection receives the first signal to time at which the first wirelesscommunication section transmits the second signal, the indicator relatedto the second wireless communication section is a period of time fromtime corresponding to the specific element in the chronologicalinformation obtained when the second wireless communication sectionreceives the first signal to time corresponding to the specific elementin the chronological information obtained when the second wirelesscommunication section receives the second signal, and in the secondprocess, the control section verifies that the specific element detectedwith regard to the wireless communication section whose calculateddifference from shortest time is a third threshold or less is based onthe pulse signal coming through the shortest path, among time serving asthe indicator related to the first wireless communication section andtimes serving as the respective indicators related to of the pluralityof second wireless communication sections.
 6. The communication deviceaccording to claim 2, wherein each of the plurality of wirelesscommunication sections receives a first signal that is the pulse signaltransmitted from the other communication device, a first wirelesscommunication section, which is one of the plurality of wirelesscommunication sections, transmits a second signal that is the pulsesignal in response to the first signal, each of a plurality of secondwireless communication sections, which are wireless communicationsections other than the first wireless communication section among theplurality of wireless communication sections, receives the secondsignal, each of the plurality of wireless communication sectionsreceives a third signal that is the pulse signal from the othercommunication device in response to the second signal, the indicatorrelated to the first wireless communication section is a period of timefrom time at which the first wireless communication section transmitsthe second signal to time corresponding to the specific element in thechronological information obtained when the first wireless communicationsection receives the third signal, the indicator related to the secondwireless communication section is a period of time from timecorresponding to the specific element in the chronological informationobtained when the second wireless communication section receives thesecond signal to time corresponding to the specific element in thechronological information obtained when the second wirelesscommunication section receives the third signal, and in the secondprocess, the control section verifies that the specific element detectedwith regard to the wireless communication section whose calculateddifference from shortest time is a fourth threshold or less is based onthe pulse signal coming through the shortest path, among time serving asthe indicator related to the first wireless communication section andtimes serving as the respective indicators related to the plurality ofsecond wireless communication sections.
 7. The communication deviceaccording to claim 2, wherein the indicator is time corresponding to thespecific element in the chronological information obtained when thewireless communication section receives the pulse signal, and in thesecond process, the control section verifies that, among timescorresponding to the respective specific elements of the plurality ofwireless communication sections, the specific element corresponding totime whose difference from earliest time is a fifth threshold or less isbased on the pulse signal coming through the shortest path.
 8. Thecommunication device according to claim 1, wherein the chronologicalinformation is a correlation computation result that is a resultobtained by correlating the pulse signal transmitted from the othercommunication with the pulse signal received by the wirelesscommunication section at designated intervals after the othercommunication device transmits the pulse signal, and includes acorrelation value indicating a degree of the correlation as the elementobtained at each timing between the designated intervals, and in thefirst process, the control section detects, as the specific element, theelement whose amplitude component included in the correlation valueexceeds a predetermined threshold for first time among the correlationcomputation results.
 9. The communication device according to claim 1,wherein the chronological information includes a result obtained bysampling the pulse signal received by the wireless communication sectionat designated intervals, as the element obtained at each timing betweenthe designated intervals, and in the first process, the control sectiondetects, as the specific element, the element whose amplitude componentof the pulse signal exceeds a predetermined threshold for first time.10. The communication device according to claim 1, wherein, in the thirdprocess, the control section extracts respective phase componentsincluded in the three or more specific elements that are verified as thespecific elements based on the pulse signal coming through the shortestpath, and estimates an angle from which the pulse signal has come on abasis of the three phase components that have been extracted.
 11. Thecommunication device according to claim 10, wherein, in the thirdprocess, the control section estimates the angle from which the pulsesignal has come on a basis of the respective phase components includedin the three or more specific elements detected with regard to the threeor more wireless communication sections that form a plane.
 12. Aninformation processing method that is performed by a communicationdevice including a plurality of wireless communication sections, each ofwhich is configured to wirelessly receive a signal from anothercommunication device, the information processing method comprising:performing a first process of detecting a specific element that is acertain element in chronological information based on respective pulsesignals received by the plurality of wireless communication sections, ona basis of respective pieces of chronological information including, asthe elements related to time, information that chronologically changesand that is obtained when the plurality of wireless communicationsections receive the respective pulse signals, which are signalsincluding a pulse transmitted from the other communication device;performing a second process of verifying whether each of a plurality ofthe specific elements detected through the first process is based on thepulse signal coming through a shortest path from the other communicationdevice to each of the plurality of wireless communication sections; andperforming a third process of estimating an angle from which the pulsesignal has come while using axes extending from reference point, whichis set to the plurality of wireless communication sections, as referenceaxes, on a basis of the plurality of specific elements that are verifiedas elements based on the pulse signals coming through the shortest pathamong the specific elements in the chronological information based onthe respective pulse signals received by the plurality of wirelesscommunication sections.
 13. A storage medium having a program storedtherein, the program causing a computer for controlling a communicationdevice including a plurality of wireless communication sections, each ofwhich is configured to wirelessly receive a signal from anothercommunication device, to function as a control section configured toperform a first process of detecting a specific element that is acertain element in chronological information based on respective pulsesignals received by the plurality of wireless communication sections, ona basis of respective pieces of chronological information including, asthe elements related to time, information that chronologically changesand that is obtained when the plurality of wireless communicationsections receive the respective pulse signals, which are signalsincluding a pulse transmitted from the other communication device,perform a second process of verifying whether each of a plurality of thespecific elements detected through the first process is based on thepulse signal coming through a shortest path from the other communicationdevice to each of the plurality of wireless communication sections, andperform a third process of estimating an angle from which the pulsesignal has come while using axes extending from reference point, whichis set to the plurality of wireless communication sections, as referenceaxes, on a basis of the plurality of specific elements that are verifiedas elements based on the pulse signals coming through the shortest pathamong the specific elements in the chronological information based onthe respective pulse signals received by the plurality of wirelesscommunication sections.